This invention relates generally to stackable lids and more particularly to stackable lids which are placed onto food containers by automated processing machinery.
Many ready-to-cook foods, such as prepackaged frozen foods, are available in microwave usable containers or plates having plastic lids fitted thereto. Such prepackaged foods are generally prepared by the manufacturer utilizing automated processing machinery which fills the containers with food, places the lids thereon, and packages the final product for freezing.
The lids commonly have notches in their rims extending about the rim periphery which provide interior locking projections to provide a snap fit of the lid to a container. Stacks of such lids are placed into in-feed bins accessible by the automated processing machinery for placement of the lids onto the containers. The lids are individually pulled from the stacks by the machinery and snap fit onto the containers. The lids are fit onto the containers in such a way that one of the locking projections is snap-locked onto the container last. The lids must be grasped by the machinery in the proper orientation so that the last projection to be fit to the container is in a predetermined position relative to the machinery. Accordingly, the lids in a given stack must be rotationally aligned with respect to the other lids and, the stack of aligned lids must be properly aligned within the in-feed bins. This will assure that the lids are taken from the stack by the machinery in the proper rotational orientation so that the one locking projection is snap-locked onto the container last.
If the stacks of lids are not properly oriented in the in-feed bins, the processing machinery is not able to snap fit the lid onto the container. When this happens, somewhere downstream in the processing line, the lid falls away from the container causing the machinery to jam or food to be dislodged from the container. This requires the process line to be shut down and may also require extensive cleaning of the machinery. Such disruptions in the process are time consuming and expensive.
Lids of the prior art are held in rotational alignment in a stack of lids by ribbing. The side walls of such lids have a ribbed and grooved outer surface which mate with the ribs and grooves in the two adjacent lids in a stack. However, the ribs do not securely keep the lids in rotational alignment. For example, it is easy for a lid to become rotationally offset from the other lids by one or more ribs. When this happens, the misaligned lid might not be properly fit onto a container resulting in the lid becoming dislodged and disrupting the process line. It is very difficult for a person to detect such a misaligned lid within a stack of lids.
Assuming the lids are all rotationally aligned within a stack, the stack itself must be rotationally aligned within the in-feed bin of the machinery. Presently, persons responsible for placing stacks of lids into the in-feed bins align the stacks by reference to an arrow or other stamped indicia on the top of the lids. A person focuses on this indicia on the lid at the top of the stack and accordingly places the stack so that the machinery grasps the lids in proper alignment. However, the arrow or other indicia is difficult to see and accordingly, makes it difficult to properly align the stacks of lids.